This invention relates to a power steering system including a power cylinder to which a hydraulic fluid delivered from an oil pump driven by an engine is supplied through a fluid-passage changeover valve.
Known power steering systems have been unsatisfactory in various respects. They fail to satisfy a variety of requirements for performance. They are unsatisfactory due to the failure to provide a light action during the travel of a vehicle at a low speed, the absence of an adequate reaction and the lack of stability for straight movement during the travel at a medium or high speed, the lack of a smooth return during the whole range of the vehicle speed, excessive rotation of a steering wheel in a case of emergency during travel at a high speed, the insufficiency of reliability in operation, the lack of assurance for safety in a case of failure, and the lack of economy of energy consumption.